ABSTRACT
The first stage of wastewater treatment is the removal of large floating objects (such as rags, maize cobs, pieces of wood) and heavy mineral particles (sand and grit). This is done in order to prevent, for example, floating material accumulating on the surface of waste stabilization ponds and heavy solids entering the pond sludge layer, and to protect from damage the equipment used in the subsequent stages of treatment (for example the floating aerators in aerated lagoons or any pumps which may be used). This preliminary treatment comprises screening and grit removal.
